1. Field of the Invention
The present invention relates to fluorescent and non-fluorescent infrared light absorbing dyes for use in filters or sensing materials and, more particularly, to thermally stable and highly soluble dyes including aminium, diimonium, or polymethine cationic chromophores having at least one absorption maximum between about 700 nm and 2000 nm and borate counterions.
2. Description of the Prior Art
There are many applications in which dyes, including infrared light absorbing dyes, when dissolved or dispersed in a host liquid, solid, or gel provide light absorption and, in some cases, fluorescent or phosphorescent light emission. For example, non-luminescent or poorly luminescent infrared dyes are used in light filters (luminescence being understood to encompass all light emission whether by fluorescence, phosphorescence, or an undetermined emission mechanism). Infrared light filters are utilized in sensors, including solid state detectors, photodiode arrays, imaging sensors, such as a charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) arrays, and other imaging devices, to shape the sensitivity curve of a broadly photosensitive element(s), e.g., by absorbing invisible light to provide a sensor sensitivity curve similar to that of the eye. Filters comprising such infrared absorbing dyes are also used to protect sensors or the eye from infrared radiation, e.g., laser radiation, or other sources of infrared light such as welding operations.
Infrared wavelength filters may also be used to diminish the intensity of the infrared light energy emitted from the sun, illumination sources, information displays, including cathode ray tubes (CRTs), liquid crystal and plasma displays, light emitting diodes, and other emissive technologies such as organic light-emitting diodes (OLEDs), especially in cases where such infrared light sources may interfere with the operation of sensors. Infrared absorbers may also be used to provide infrared blocking in otherwise infrared transparent or partially infrared transparent plastic articles, e.g. banking or credit cards, in which visibly partially transparent plastics provide for marketing or security features. Infrared dyes may also be used in cell biology applications, in inks, or in heat activated compositions.
In addition to these and other applications of non-emissive infrared dyes, emissive infrared dyes are used, for example, in laser devices and laser applications, in security inks, in sensors, and in biological or medical analyses. The infrared emissive dyes may also be used in inks or heat activated compositions.
Infrared absorbing and emitting dyes have a long history and thousands of compositions are known. The often fluorescent polymethine class of chromophores were among the first infrared dyes. Infrared absorbers may also be categorized into several other classes of chemical compounds including, among others, the phthalocyanines and their metal complexes, naphthalocyanines and their metal complexes, anthraquinone derivatives, dithiolenes (also known as metal complex dyes), aminium salts, and diimonium salts. Of these, generally some polymethines, some phthalocyanines, and some naphthalocyanines have infrared emission. Also, polymethines and unsubstituted phthalocyanines and naphthalocyanines have relatively narrower absorption spectra than dithiolenes, anthraquinone derivatives, aminium salts or diimonium salts. Both narrow and broad band absorbers are useful because each has performance advantages in certain applications.
The first report of the spectral properties of infrared light absorbing aminium dyes was by Otto Neunhoeffer and Peter Heitmann (See Neunhoeffer et al., Chemische Berichte 92, 245-251 (1959)). Subsequent development of these dyes at the American Cyanamid Company of Stamford, Conn. by Peter Susi and colleagues is reported in the patent literature (See U.S. Pat. Nos. 3,341,464, 3,440,257, 3,484,467, 3,575,871, and U.S. Pat. No. 3,631,147 to Susi et. al., U.S. Pat. No. 3,400,156 to Milionis et al., and U.S. Pat. No. 3,962,290 to Grosso). Various other patents disclose methods of preparation of intermediates and the use of such aminium salts as infrared absorbing components of light filters.
The limited thermal stability of the aminium and related diimonium salts was immediately recognized. Studies showed that the hexafluoroantimonate (SbF6−) and, to a somewhat lesser degree, hexafluoroarsenate (AsF6−) salts of the aminium ions, as shown in Table I below taken from U.S. Pat. No. 3,341,464 to Susi et al., were the most stable, i.e., these salts showed the greatest retention of optical density upon exposure to high temperature.
TABLE IRelative Thermal Stability of Representative Aminium SaltsPercent Remaining after 8Anionminutes in a 200-205° C. oil bathSbF6−76AsF6−70ClO4−49p-CH3C6H4SO3−37.6BF4−25F−23.5EtSO3−19.5CF3CO2−4.2NO3−0
Therefore, it is not surprising that the most thermally stable hexafluoroantimonate salts of both the aminium and diimonium chromophores have been widely used as infrared absorbing components. Note, however, that the thermal decomposition of certain diimonium salts can, in some cases, be useful in some applications. For example, U.S. Pat. No. 5,686,639 to Cohen discloses the use of quinone diimonium hexafluoroantimonate salts as epoxy curing agents. The diimonium dyes are much less thermally stable than the aminium compounds.
The limited solubility of polymethine, aminium, and diimonium salts containing counterions such as hexafluoroantimonate, hexafluoroarsenate, perchlorate, hexafluorophosphate, tetrafluoroborate, tosylate, etc., is most apparent in applications that require high optical densities in a low polarity host. For example, IR-140, a commercially available infrared dye, has very limited solubility in toluene or polystyrene as its perchlorate or tosylate salt. Another example is the low solubility of tris(4-diethylaminophenyl)aminium SbF6− in a soft contact lens. Here is an example where the required thickness of the part, i.e., the contact lens, is constrained by the application to only on the order of 100 micrometers and, yet, the optical density requirements for infrared light protection can be high. High solubility is therefore required.
More than 20 years after the reported work at the American Cyanamid Company, Frederic Castellanos and his colleagues (hereinafter Castellanos), who were working in applications unrelated to infrared dyes, described a series of ultraviolet light absorbing photoinitiators that were paired with electron poor borate anions, which they termed “onium borates.” Specifically, U.S. Pat. Nos. 5,468,902, 5,550,265, 5,668,192, and 6,147,184 to Castellanos et. al., all titled “Onium Borates/Borates of Organometallic Complexes and Cationic Initiation of Polymerization Therewith,” describe the compositions and use of UV-absorbing onium borates as cationic polymerization initiators. In addition to absorbing in different parts of the electromagnetic spectrum than the infrared dyes described herein, the onium solution and polymer chemistry described by Castellanos is significantly different from the chemistry of aminium, diimonium, and polymethine dyes. Whereas as Castellanos' UV-absorbing onium salts, as described, are cationic polymerization initiators, many infrared dyes, including the aminium radical salts, are polymerization inhibitors.
Castellanos' fundamental discovery was that onium salts comprised of specific borate anions were at least as effective at catalyzing cationic polymerization as the corresponding onium salts of hexafluoroantimonate anions, and more effective catalysts than the onium salts of, for example, hexafluorophosphate anions. However, Castellanos did not remark on thermal stability or solubility of his onium borates.
One of the most desirable plastics or polymers for use in light filters is polycarbonate. Polycarbonate, also frequently referred to by the General Electric Company trademark Lexan®, can be formulated and molded into various shapes in high temperature processes. Polycarbonate's combination of optical and mechanical properties often makes this material the polymer of choice for ophthalmic as well as other applications. The difficulty of molding aminium infrared absorbers into polycarbonates is well known and is related to the decomposition of these dyes at the relatively high temperatures required to mold polycarbonate. Although non-impact resistant polycarbonate grades may be molded at lower temperatures where the aminium hexafluoroantimonates decompose relatively slowly, molding of impact resistant polycarbonates normally requires barrel temperatures above about 500° F. At these temperatures, even the most thermally stable aminium hexafluoro-antimonates decompose relatively rapidly and consistent molding results can be difficult to obtain.
Furthermore, despite their limited thermal stability and, therefore, their limited utility in higher temperature, higher performance transparent resins, such as lower melt flow index grades of polycarbonate, improvements in the thermal stability of aminium salts have not been reported in over 35 years. Perhaps researchers believed that the thermal stability of the most stable hexafluoroantimonate aminium dyes was limited not by the nature of the anion, but by the stability of the cation itself, or by reaction of the cation with the host liquid or polymer at melt processing temperatures.
One path to a solution to fabricate polycarbonate light filters that reduces the thermal decomposition of the previously described aminium dyes has been the development of polycarbonate blends that can be processed at temperatures where the aminium SbF6− dyes decompose relatively slowly. Such polymer compositions or blends have been disclosed, for example, in U.S. Pat. Nos. 5,210,122 and 5,326,799 to L. P. Fontana et al., and U.S. Pat. No. 5,434,197 to L. A. Cohen. However, one disadvantage of this approach is that the haze of at least one such material, e.g., General Electric Company's Xylex® X7200, is higher than that of unblended, ophthalmic or “OQ” grade polycarbonates. Therefore, this polymer blend approach has limitations for impact resistant filters in optical filter applications.
More recently, absorptive dyes have also been combined with reflective or diffractive elements, e.g., rugates, dielectric stacks, holograms, and other types of coatings that provide complementary or supplementary filtration of wavelengths or wavelength bands, in order, for example, to fabricate highly effective optical filters. The deposition of these coatings may result in substrate temperatures that exceed the distortion temperatures of the non-impact resistant grades of polycarbonate. Therefore, it is desirable to provide absorbing substrates in higher temperature grades of polycarbonate in applications where dyes and coatings are both used.
Accordingly, one objective of the present invention is to provide infrared light absorbing dyes that are capable of absorbing light in the range of about 700 to 2000 nm.
It is another objective of the present invention to provide infrared light absorbing and light emitting light filters, materials, films, solutions, coatings, or inks.
It is another objective of the present invention to provide infrared light absorbing dyes that can be processed at high temperatures, e.g., in polycarbonate molding operations.
It is another objective of the present invention to provide infrared light absorbing dyes that are soluble in non-polar or low polarity solvents or polymers.
It is another objective of the present invention to provide a light filter, material, film, solution, coating or ink that is capable of absorbing light in the range of about 700 to 2000 nm.
It is another objective of the present invention to provide a light filter, material, film, solution, coating or ink that transmits a substantial portion of light at visible wavelengths.
It is another objective of the present invention to provide aminium and diimonium dyes with greater thermal stability than those comprised of hexafluoroantimonate anions.
It is another objective of the present invention to provide aminium and diimonium dyes with greater solubility in non-polar hosts than those comprised of hexafluoroantimonate anions.
It is another objective of the present invention to provide polymethine dyes with greater solubility in non-polar hosts than those comprised of perchlorate or tosylate anions.
It is another objective of the present invention to prepare infrared light absorbing cationic dyes with counterions that lack potentially toxic anions such as perchlorate or toxic heavy atoms, e.g. antimony or arsenic.
It is another objective of the present invention to provide light filters capable of filtering out undesirable, harmful, or dangerous wavelengths of infrared light.
It is another objective of the present invention to prepare filters for electromagnetic radiation, including laser radiation, that are comprised of thermally stable infrared absorbing dyes, alone, or in combination with other absorbing dyes, stabilizers, or other non- or weakly visible light absorbing additives such as UV-absorbers, light stabilizers, anti-oxidants or free radical trapping agents.
It is another object of the present invention to prepare filters for electromagnetic radiation, including laser radiation, that are comprised of highly organic-soluble infrared absorbing dyes, alone, or in combination with other absorbing dyes, stabilizers, or other non- or weakly visible light absorbing additives such as UV-absorbers, light stabilizers, anti-oxidants or free radical trapping agents.
It is another objective of the present invention to prepare filters for electromagnetic radiation in forms such as spectacles, visors, and contact lenses.
It is another objective of the present invention to prepare dyes that are chemically, thermally, and photochemically compatible with optical filter, material, film, solution, coating or ink manufacturing processes, and with processes for depositions of subsequent coatings, if any. Such processes may include molding, casting, imbibing, thermal curing, and radiation or UV curing, among others.
It is another objective of the present invention to improve the manufacturing-related metrics of reproducibility and consistency of the transmittance and optical density of filters, materials, films, solutions, coatings or inks containing infrared absorbing dyes.
It is another objective of the present invention to reduce the cost of manufacturing infrared absorbing filters by minimizing the additional amount of dye that is often required to make up for decomposition of less thermally stable infrared absorbing dyes.
It is another objective of the present invention to increase the luminous transmission of infrared absorbing filters, materials, films, solutions, coatings or inks by reducing the decomposition of thermally sensitive infrared absorbing dyes.
It is another objective of the present invention to provide filters, materials, films, solutions, coatings or inks comprising infrared absorbing dyes from plastic resins that are compatible with processes used to deposit coatings on polymeric substrates.
It is another objective of the present invention to provide filters from plastic resins that are optionally impact resistant. Such plastic resins and filters are optionally polycarbonate. Such plastic resins and filters are optionally of ophthalmic quality. Such plastic resins and filters optionally offer impact or ballistic protection. The filters, films, or substrates may be in any shape useful to their end-purpose, e.g., a curved lens or visor for eye protection or a flat sheet for a vision system.
It is another objective of the present invention to develop a process for and provide filters in the form of a contact lens. Such contact lens resins may include polymethylmethacrylate (PMMA), poly(beta-hydroxyethyl methylmethacrylate), or any high oxygen permeability polymer. The filters, films, or substrates may be in any shape useful to their end-purpose, i.e., standard diameter or oversize to protect the cornea, and scripted as required for the individual.
It is another objective of the present invention to prepare notch, long pass, short pass, and band pass filters for optical filter applications by substituting known infrared absorbing dyes with at least one of the dyes disclosed herein into or onto a substrate that is optionally compatible with absorptive and/or diffractive and/or reflective coatings and coating processes.
It is another objective of the present invention to provide infrared absorbing and/or infrared emitting products for materials including polystyrene and other low polarity materials that find use in cell biology applications.
The present invention achieves these objectives and addresses the weaknesses and drawbacks of previously proposed infrared dyes by providing infrared dye compositions comprising polymethine, aminium, or diimonium borate salts, and related compositions, having greater thermal stability in molding and greater solubility, which is most apparent in non-polar solvents and hosts. These compositions are useful in a variety of applications, including those where high transmittance across much of the visible light spectrum and low transmittance at certain wavelengths in the infrared are required. For example, the compositions may be used in information displays such as holographic displays, as filters for laser radiation, as filters for illumination sources, as filters for photographic processes, and as filters for light emitting diodes including organic light emitting diodes, in security inks, in eye protection including contact lenses, and in sensors, including infrared fluorescent sensors of all types.